About this world
HD 168009 b is a sub-Neptune orbiting HD 168009, a yellow, Sun-like star (type G2V) 76 light-years from Earth. It is about 3 times the size of Earth (its size estimated from its mass), with at least 9.5 Earth masses (a minimum, measured by radial velocity). It completes an orbit every 15.1 days at 0.12 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 888 K (614 °C): far too hot for liquid water on its surface. At its size it almost certainly keeps a deep envelope of hydrogen and helium.
It was discovered in 2021 by radial velocity with Multiple Observatories. The star wobbles toward and away from us, Doppler-shifting its spectrum.